Typically, wet, lead-acid batteries have a right rectangular shaped container and a cover assembly, both parts usually being made of an injection molded thermoplastic polymer, such as polypropylene. The interior of the container frequently is divided by partition walls into cells, and each cell is substantially isolated. Electrode stacks are disposed within each cell and are electrically connected in series. Each cell is filled with electrolyte to a level at least equal to the top of the electrode stack. When the battery is designed to be maintenance free, however, it is preferable that the electrolyte level significantly exceed the top of the stacks.
Such lead-acid storage batteries generate gases, predominantly hydrogen and oxygen, during charging. The presence of hydrogen and oxygen gas creates an obvious potential for explosion, and therefore, those gases must be vented from within the battery to the ambient. Accordingly, wet lead-acid batteries are equipped with a venting system. The venting system must permit substantially complete evacuation of generated gases and, as a generally recognized standard in the industry, within eight hours.
In wet batteries, particularly in maintenance-free wet batteries, there are large quantities of free electrolyte in the cell. That electrolyte can slosh and splash about the interior of the battery during shipment, installation and use of the battery. Moreover, the battery, usually because the vehicle in which it is mounted is so inclined, may be tilted at severe angles which can encourage electrolyte to pass through the venting system. The venting system, therefore, not only must allow gases to vent. It also must prevent electrolyte from escaping, even when the battery is tilted severely and especially in maintenance-free batteries where replenishment of electrolyte is not contemplated.
The venting system generally is located within and defined by the cover assembly, e.g., a primary and secondary cover or a primary cover and one or more cover pieces. Typically, it comprises an internal drain/vent aperture, a trapping chamber and an external exhaust port. The internal drain/vent aperture, typically a vertically oriented, circular or doughnut shaped hole or slits with horizontal and vertical components, is designed such that electrolyte which has entered the trapping chamber may drain through it back into the cell. It also is designed to allow venting of gases while minimizing the passage of electrolyte from the cell into the trapping chamber. The design of drain/vent apertures is illustrated, e.g., in U.S. Pat. No. 4,486,516 to D. Poe (slit with vertical and horizontal components); U.S. Pat. No. 4,371,591 to T. Oxenreider et al. (vertically oriented, circular shaped hole); U.S. Pat. No. 4,002,495 to D. Hakarine (vertically oriented, circular shaped hole); and U.S. Pat. No. 3,666,564 to R. Corbin et al. (vertically oriented, doughnut shaped hole). Some designs incorporate a vent aperture as well, which is designed to allow venting of gases, especially when the drain/vent aperture may be clogged with electrolyte. Such designs are illustrated, e.g., in Poe '516.
The drain/vent aperture, and if present, the vent aperture, open into a trapping chamber which permits gases to pass to the exhaust port. The trapping chamber, however, generally by utilizing sloped floors and a variety of baffle arrangements, is designed to allow condensation of electrolyte vapors and to prevent electrolyte which has entered the chamber through the drain/vent aperture and/or vent aperture from reaching the external exhaust port. It is constructed such that electrolyte collected in the chamber drains through the drain/vent aperture and back into the cell.
The space between the electrolyte level and the top of the battery cover, however, (in which all or part of the trapping chamber is located) is wasted in the sense that it is in no way utilized for the electrochemical performance of the battery. The external dimensions of automotive batteries are largely dictated by convention, i.e., by vehicle manufacturers. In order to achieve the maximum electrochemical performance within given dimensional constraints, such wasted space must be kept to a minimum.
Recombinant or absorbed electrolyte, as opposed to wet, batteries also generate hydrogen and oxygen during charging. Unlike wet batteries, however, the gases evolved in a recombinant battery are substantially induced to recombine within the battery. Accordingly, recombinant batteries are not equipped with a venting system per se. They instead are equipped with a pressure release system, generally comprising a pressure relief valve, which is in communication with the ambient and prevents excessive pressure from building in the battery interior. Examples of such pressure release systems and valves are disclosed, e.g., in U.S. Pat. No. 4,328,290 to J. Szymborski et al. The venting systems incorporated in cover assemblies for wet batteries, however, typically preclude a facile and reliable conversion to a pressure release system. If substantially the same cover assembly could be used to manufacture both wet and recombinant batteries, significant cost savings would be realized.
The venting system, therefore, must be designed to completely and efficiently vent gases and minimize electrolyte escape, even when the battery is tilted at severe angles. It also should be designed so that the wasted space in the battery is minimized. Preferably, its design should be simple and permit easy construction, assembly, and, if desired, conversion of the cover assembly for use in recombinant batteries as well. Unfortunately, conventional designs have not succeeded in achieving all of those objectives simultaneously.
Essentially, there are two types of battery venting system designs commonly in use. They are described as either vertical-type or horizontal-type depending on the orientation of the trapping chamber used. Discrete vent plugs found on many batteries exemplify vertical-type venting systems. The plugs typically include a deep, cylindrical chamber which fits tightly into the filler well of the battery cells. Separation of the electrolyte from the gas occurs primarily by gravity as the gases rise vertically through the cylindrical chamber and the heavier electrolyte falls to the chamber floor. The floor of the chamber slopes toward a central drain/vent aperture through which the gases can pass upwardly and the electrolyte can drain back into the cell. The top of the chamber has an exhaust port for discharging the gases to the atmosphere. The chamber also may contain a variety of internal baffles to aid in preventing electrolyte from reaching the exhaust port. Examples of vertical venting systems are illustrated, e.g., in Hakarine '495. Vertical-type vent systems generally can be effective in venting gases and preventing electrolyte from escaping, but in doing so, may tend to occupy large amounts of wasted space. Additionally, conversion of the typical, vertical-type cover assembly for use in a recombinant battery at the very least would require equipping the assembly with six pressure release valves, an obvious and undesirable expense.
Horizontal-type vent systems, on the other hand, typically include an elongated trapping chamber extending horizontally across at least part of the top of each battery cell. The drain/vent aperture usually is located laterally remote from the exhaust port. Electrolyte entering the chamber must traverse the length of the chamber, and typically a variety of baffles as well, in order to reach the exhaust port, and the floors of the chamber are sloped to encourage return drainage of the electrolyte into the cell. The drain/vent aperture, however, usually is located elevationally much closer to the exhaust port then in vertical vent systems. Horizontal type venting systems are illustrated, e.g., in Poe '516; U.S. Pat. No. 4,444,853 to V. Halsall et al.; Oxenreider '591; and Corbin '564. The chamber height, i.e., the distance between the drain/vent aperture and the exhaust port being reduced, generally there is less wasted space in horizontal type venting systems.
The typical automotive battery, however, comprises six cells, and horizontal venting systems for those batteries necessarily are quite complex. Although it is common to manifold the trapping chambers, i.e., to allow mixing of gases between a plurality of trapping chambers, and thereby utilize fewer exhaust ports, each cell still must be provided with its own drain/vent aperture and trapping chamber. Manifolded trapping chambers and the general complexity of horizontal venting systems are illustrated, e.g., in Poe '516, Halsall '853, Oxenreider '591, and Corbin '564. Thus, horizontal venting systems remain complex, and due to the necessary complexity of the pieces from which they are assembled, difficult to mold and assemble.
The general complexity of most horizontal venting systems and the large amounts of horizontal space which they tend to occupy also creates problems if other features are needed in the battery. For example, it is difficult, impractical, or impossible to accommodate dual terminals, i.e., both side and top terminals, or a recessed, slidable handle in cover assemblies comprising many conventional horizontal venting systems.
Additionally, most horizontal venting systems do not permit the cover assembly to be converted easily for use in recombinant batteries. Typically the conversion is not feasible due to the complexity of the venting system design and, even if not otherwise foreclosed, would require six pressure release valves.
Many horizontal venting systems also do not efficiently vent gases, a major cause of which is pockets defined in the elaborate contours of the cover assembly undersurface. Hydrogen tends to rise. Although Brownian motion may prevent large quantities of hydrogen from being trapped therein, such pockets do tend to impede the flow of gases to the drain/vent aperture and/or vent aperture and thus to the ambient.
Some horizontal-type vent systems utilize a so called "raised" design, in which the exhaust ports and part or all of the trapping chambers are situated above the cover surface. Raised, horizontal venting systems are illustrated, e.g., in Poe '516. The effective chamber height in such designs generally is reduced (by locating the exhaust port above the cover surface), and therefore, raised vents often further reduce the amount of wasted space. Raising the venting system, however, does nothing to reduce the wasted space between the drain/vent aperture and the electrolyte level. Primarily because of the orientation and shape of their drain/vent apertures, horizontal venting systems, including raised vent systems, still must be mounted at a substantial distance above the electrolyte, and even then, many designs tend to leak electrolyte when tilted.
Although raised horizontal vents may be preferred for reducing in part the amount of wasted space, unlike flat top designs, they tend to constrain the degree of standardization which the battery can achieve. That raised top batteries interfere with standardization, i.e., the attempt to make a single battery design compatible with the requirements imposed by as many automobile designs as possible, can be understood by considering, inter alia, the various devices which are used to mount the battery in the vehicle. Examples of such include molded heat shields and horizontally overlaid bars, plates, and L shaped restraints. It is well known, however, that the surface geometry of raised vent systems can interfere with mounting devices and make a battery suitable for one type of vehicle unsuitable for another.
Furthermore, even with flat top designs, standardization is made more difficult because many conventional mounting devices cannot be adjusted to accommodate the variation in external dimensions among batteries. The external dimensions of batteries, as noted above, are dictated by vehicle manufacturers. The more common variations involve battery height, there being a high profile (approximately 8") and a low profile (approximately 71/4"), and battery width, there being a narrow (approximately 61/2"), a standard width (approximately 7"), and a wide (approximately 71/4"). In an effort to achieve greater standardization, manufactures have provided smaller batteries with height and/or width spacers to make them compatible with mounting devices designed for larger batteries, e.g., to adapt a low profile battery to high profile battery mounting devices or a standard width battery to wide battery mounting devices. Such spacers generally have been H shaped and aligned longitudinally across the horizontal center line of the cover, but have proven unsatisfactory for adapting the batteries to a sufficiently large number of conventional mounting devices. For example, they do not successfully adapt a low profile battery to a non-vertically adjustable, high profile battery mounting device which comprises molded heat shields. Examples of H shaped, top spacers for modifying battery height or width have been commercialized by GNB Incorporated, Mendota Heights, Minn. 55118.
Finally, whereas flat top designs are desirable in that they allow greater standardization, they typically preclude stacking of top terminal batteries, i.e., batteries having terminals on the top surface of their cover assembly. Stacking is desired not only for convenience in handling, but also because it allows retailers to build displays. Some top terminal batteries, however, are stackable. Stackable designs typically raise portions of the cover assembly to the level of the top terminals, which as noted above, can interfere with efforts to standardize the battery for the wide variety of conventional mounting devices, or removably connect the terminals to the battery, which can compromise the conductivity and durability of the terminals. Moreover, neither design allows for sufficient stability in large stacks of batteries. Stackable designs are illustrated, e.g., in U.S. Pat. No. 4,448,863 to C. Terrell (removably connected terminals); U.S. Pat. No. 4,424,264 to M. McGuire et al. (raised cover assembly portions); and U.S. Pat. No. 3,871,924 to D. DeMattie et al. (raised cover assembly portions).
In summary, while horizontal venting systems present an improvement over vertical vent systems, they remain complex in design, difficult to make and assemble, and yet do not always provide for complete evacuation of gases or prevent electrolyte from escaping, especially when the battery is tilted. Moreover, their design often interferes or precludes incorporating dual terminals and/or recessed, slidable handles and is not modified easily or economically for use in recombinant batteries. Conventional horizontal venting systems also must be situated so that their drain/vent aperture is located a significant distance above the electrolyte level and, therefore, contribute to wasted space in the battery, even in a raised design. In raised designs, however, the venting system interferes with attempts to standardize the battery. Finally, although more susceptible to standardization than raised designs, flat top batteries, even with known spacers, fail to achieve a satisfactory degree of standardization and/or are not stackable.
An object of this invention, therefore, is to provide a horizontal venting system which performs efficiently yet which is simple in design, construction, and assembly.
A further object of this invention is to provide a horizontal venting system which can be mounted closer to the electrolyte level and thereby reduce the amount of wasted space in the battery.
Another object of this invention is to provide a horizontal venting system which permits substantially all generated gases to vent to the atmosphere within eight hours.
A further object of this invention is to provide a horizontal venting system which prevents electrolyte escape even when the battery is tilted at severe angles.
Another object of this invention is to provide a horizontal venting system such that the cover assembly in which it is defined can accommodate easily dual terminals and/or recessed slidable handles.
A further object of this invention is to provide a horizontal venting system for a wet battery which can be modified readily and economically such that the cover assembly in which it is defined can be used in recombinant batteries.
Yet another object of this invention is to provide a low profile, flat top battery, especially one having top terminals, with a spacer such that the battery is compatible with high profile battery mounting devices and is stackable.
Another object of this invention is to provide a narrow or standard width battery with a spacer such that the battery is compatible with mounting devices designed for wider batteries.
Other objects of the present invention will become apparent from the following description.